1. Field of the Invention
The present invention relates to a charged particle beam apparatus for processing a sample by using a focused ion beam.
2. Description of the Related Art
As semiconductor devices become more finely patterned, there has been increasing importance placed on a technology which uses a transmission electron microscope (TEM) to observe and analyze a minute area of the device. When the TEM is used to make an observation, it is necessary to process the minute area into a sample lamella having such a thickness that allows an electron beam to be transmitted therethrough. For the fabrication of the sample lamella, a focused ion beam apparatus has been widely used. However, when a sample lamella is fabricated using the focused ion beam apparatus, there is a problem that a damaged layer is formed in the sample lamella due to irradiation of the focused ion beam.
One known method for solving this problem is to employ an apparatus in which the focused ion beam apparatus is provided with an argon-ion beam irradiation unit (see Japanese Patent Application Publication No. 2007-66710).
With this method, a damaged layer formed due to the irradiation of the focused ion beam is irradiated with an argon-ion beam from an appropriate angle, thereby performing removal processing.
Further, another known method is to fabricate a sample lamella by using a focused ion beam accelerated with a low acceleration voltage. With this method, the thickness of a damaged layer formed in the sample lamella can be made smaller. However, when the focused ion beam is accelerated with a low acceleration voltage, chromatic aberration of the ion beam optical system becomes larger. For this reason, the beam diameter of the focused ion beam cannot be made small, which is problematic.
As a method for solving this problem, there is known a method involving the employment of a focused ion beam column including an intermediate acceleration tube (see Japanese Patent Application Pubrication No. 2007-103108).
With this method, it is possible to reduce chromatic aberration of the optical system, and also to allow the focused ion beam having small energy to reach the sample.
Further, still another known method is the retarding method in which a voltage is applied to the sample. With this method, the energy of the focused ion beam is reduced immediately before the focused ion beam reaches the sample, and hence aberration can be made smaller.
However, the conventional apparatuses have the following problems.
Specifically, the configuration of the apparatus provided with the argon-ion beam irradiation unit is complex. Further, in the case of the apparatus provided with the focused ion beam column including the intermediate acceleration tube, the structure of the column is complex. Further, in the case of using the retarding method, it is necessary to form an electric field which is symmetric with respect to the focused ion beam, between the focused ion beam column and the sample. However, if the apparatus is provided with an electron beam column for sample observation, the electric field in the vicinity of the sample becomes asymmetric. Thus, the retarding effect cannot be obtained.